$ { {1} \times \left[\begin{array}{r}{1} \\ {-1} \\ {-2}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{1}\times{1} \\ {1}\times{-1} \\ {1}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{1} \\ {-1} \\ {-2}\end{array}\right]}$